A conventional body hair depilating treatment (treatment for retarding or lowering the regrowth of hair) was performed by burning out hair roots by an electrical needle. This treating method must treat hair one by one, taking a very long treating time and causing pain during treatment. Therefore, a laser depilating treatment is now being used instead of the depilating treatment using the electrical needle.
The laser depilating treatment is a treatment which retards the regrowth (growth) of hair by giving thermal or physical damage to a germinative cell and hair papilla of a hair bulb at the hair root and also to a bulge and a sebaceous gland with a laser beam. For the conventional laser depilating treatment, various types of laser irradiation devices such as a YAG laser (oscillation wavelength: approximately 1064 nm), a ruby laser (oscillation wavelength: approximately 694 nm), an alexandrite laser (oscillation wavelength: approximately 755 nm) and a semiconductor laser (oscillation wavelength: approximately 800 nm) as described in, for example, Japanese National Stage Laid-Open Publication No. 2001-500529 (International Publication No. WO98/48716) are used.
Among them, a depilating treatment apparatus using the YAG laser or the ruby laser is an apparatus which irradiates a skin surface with a high power laser beam to directly destroy (e.g., thermolysis) a hair root, a germinative cell and the like. A laser beam of the YAG laser or the like has a long wavelength and poor absorption efficiency by melanin in a hair root and germinative cell, and its power is high, so that its irradiation time per irradiation is limited. Besides, the depilating treatment apparatus using the YAG laser utilizes a very expensive medical laser irradiation device, and the depilating treatment must be performed as medical treatment.
Meanwhile, a laser depilating apparatus using a small and inexpensive semiconductor laser (laser diode) has a low power (e.g., approximately 0.01 to 10 W) laser beam emitted from the semiconductor laser, so that the laser depilating treatment can be performed as cosmetic treatment. The semiconductor laser beam has a wavelength of, for example, approximately 780 to 810 nm. This laser beam having such a wavelength is hardly absorbed by water or blood but has very high absorption efficiency by melanin in a hair root (hair shaft) and a germinative cell. Thus, the regrowth (growth) of hair can be retarded efficiently by thermal energy of the laser beam absorbed by the melanin.
As described above, the laser depilating apparatus using the semiconductor laser has a feature that the semiconductor laser beam has a wavelength suitable for the depilating treatment. However, the conventional laser depilating apparatus does not have an irradiation time, irradiation energy and other various kinds of conditions for irradiation of the semiconductor laser beam examined adequately or decided, so that an adequate depilating effect cannot be obtained depending on the situation or hair is reversely grown.
For example, Japanese Patent Unexamined Publication No. 2000-201726 describes a laser depilating apparatus which is comprised of a semiconductor laser having light power of 5 to 1000 mW, light power adjusting means for adjusting the light power of the laser beam emitted from the semiconductor laser, and irradiation time setting means for setting an irradiation time of the laser beam. Here, the light power of the laser beam is adjusted by the on-time of the laser pulse, so that thermal energy based on the irradiation of the laser beam might not be conducted effectively to the entire hair follicle tissue. Besides, there is no suggestion about an energy density or the like of the laser beam effective for the depilating treatment.
Japanese Patent Unexamined Publication No. 2001-46141 describes a laser depilating apparatus which is comprised of a laser diode for irradiating a laser beam, a control section for controlling an irradiation time of the laser beam and an output control circuit for adjusting a voltage or a current applied to the laser diode. But, the above publication does not describe specific power of the laser beam (semiconductor laser beam), an irradiation time or an energy density of the laser beam effective for depilating treatment.
Japanese Patent Unexamined Publication No. 2000-245525 describes laser therapy equipment using an alexandrite laser (oscillation wavelength: approximately 755 nm) having a wavelength similar to that of the semiconductor laser. Here, it is shown that the laser beam power is generally in a range of 10 to 40 J/cm2 (0.1 to 0.4 J/mm2). However, the alexandrite laser has the same high power as the YAG laser does, so that its laser irradiation time is limited to 10 to 40 msec. Besides, the high power alexandrite laser directly destroys (cauterizes) a hair root and the like in the same way as the YAG laser to perform the depilating treatment, so that the depilating treatment cannot be performed by conducting the thermal energy of the laser beam to the entire hair follicle tissue like the semiconductor laser.
In addition, the conventional laser depilating apparatus is difficult to increase an irradiated area per treatment with the laser beam while keeping the energy density effective for depilating. Japanese Patent Unexamined Publication No. 2000-217938 describes a laser depilating apparatus having a plurality of semiconductor lasers (laser diodes) which are circularly disposed. By using the plurality of semiconductor lasers, an irradiation area of the laser beam is increased. But, the plurality of semiconductor lasers circularly disposed are limited from increasing the irradiation area of the laser beam, and if the irradiation area is excessively increased, the laser beam might have a nonuniform energy density.
Therefore, it is desired to increase an irradiation area of the semiconductor laser beam so to improve the depilating effect of the semiconductor laser beam. There is some consideration being made on disposition of many laser diode elements in an array shape to use a semiconductor laser having high power equivalent to that of the YAG laser. But, such a laser irradiation device has variations in power density because the laser beams emitted from the individual diode elements cause interference with each other. And, because the semiconductor laser beam is designed to have high power, the feature of the semiconductor laser beam that the absorption efficiency by melanin is high cannot be utilized fully.
The present invention is to provide a laser depilating method and laser depilating apparatus which can provide a laser depilating effect more securely and efficiently by utilizing the feature of the semiconductor laser beam that the absorption efficiency by melanin in hair shafts and germinative cells is high. Besides, it also provides a laser depilating apparatus having a treatment region increased and a treatment speed improved while keeping the depilating effect of the semiconductor laser beam.